The present invention relates to apparatus and methods for operating a fluidized bed reactor having a separator for separating entrained solid particles from the flue gas and recycling the separated particles to the reactor chamber. Particularly, the separated recycled particles are fluidized before reentry into the reactor chamber and conveyed to reactor chamber inlets for even distribution of the recycled particles along the chamber bed.
Fluidized bed reactors having separators, for example of the cyclone type, for separating entrained solid particles from flue gas and recycling the separated particles back to the combustion chamber of the reactor are well known. Examples of such systems are set forth in U.S. Pat. Nos. 4,522,154 and 4,442,797. In the former patent, the particles separated in the cyclone separator are recycled to the reactor through a loop seal which prevents backflow of gas from the combustion chamber to the cyclone separator. In U.S. Pat. No. 4,442,797, fuel is supplied to the separated particles as these particles are recycled back for flow into the combustion chamber of the reactor.
In general, however, it is difficult to obtain even distribution of the separated recycled particles upon their return to the combustion chamber of the fluidized bed reactor. It will be appreciated that the recycled particles include unburned solid fuel. From an efficiency standpoint, it is desirable to distribute that unburned fuel and other particles evenly throughout the combustion chamber. This is particularly difficult in fluidized bed reactors which have large cross-sectional areas. Thus, as the recycled particles are introduced through one wall of the reactor chamber, there will be areas of the combustion bed, particularly in large reactors, which will not receive any of the separated particles or which will receive such separated particles, but to a lesser extent than other areas of the chamber.
It is possible to provide additional cyclone separators for use with a fluidized bed reactor whereby the separated particles from the respective separators may be disposed in the combustion chambers at different locations. However, while this permits the construction of fluidized bed reactors of substantial size, the costs of the cyclone separators practically limit the employment of such system as a solution to the problem of uneven distribution of the recycled separated particles in the combustion chamber. Moreover, the problem of distribution in the reactor chamber is exacerbated when it is realized that fuel should be added to the recycled separated particles to promote uniformity of combustion in the chamber.
According to one aspect of the present invention, there is provided a method of operating a circulating fluidized bed reactor having a separator for removing entrained solid particles from the flue gas including the steps of conducting the particles separated in the separator for flow from the separator into a chamber. In the chamber, the separated particles are fluidized and divided into separate particle streams. The separate particle streams are then introduced into the fluidized bed reactor at different inlet locations to distribute the separated particles substantially evenly along the fluidized bed reactor. Preferably, fuel is mixed into each of the streams of separated particles prior to their entry into the combustion chamber. The fluidization of the separated particles in the chamber includes injecting a fluid, for example air, into the chamber to maintain the separated particles in a fluidized state. The fluid injected into the fluidizing chamber serves also to assist in conveying the separated particles from the fluidizing chamber into the combustion chamber through conduits in which fuel may be introduced. Thus, in accordance with this method, the separate particle streams may be introduced at longitudinally spaced locations along the length of any wide wall of the fluidized bed reactor on any wall whereby substantial even distribution of the separated particles and fuel mixture is achieved.
According to another aspect of the present invention, there is provided an apparatus enabling the even distribution of the separated recycled particles in a fluidized bed combustion chamber. Preferably, such apparatus includes a reaction chamber, a discharge means for removing a flue gas with entrained solid particles from the reactor chamber, a cyclone separator connected to the discharge means for separating the solid particles from the flue gas, together with means for recycling at least a portion of the separated particles to the reactor chamber, including a loop seal having means for dividing at least a portion of the separated particles into separate particle streams and connecting the particle streams to the reactor chamber. In this preferred embodiment of the present invention, a pair of separators are provided, each having its lower end connected by a standpipe with a distribution chamber comprised of a generally horizontally extending duct, the standpipe and the duct forming essentially a T-connection. Conduits extend upwardly from the opposite ends of each duct, terminating in inclined conduits for connection with the combustion chamber. Plenum chambers are provided below the duct and nozzles and provide fluidizing gas, for example air, into the duct to maintain the separated particles received from the separators in a slow fluidized state. Thus, the fluidized separated particles are transmitted by the action of the inlet fluid through the end conduits into the inclined conduits. Fuel inlet ports are provided in the inclined inlets whereby the fuel and separated particles are mixed and conveyed to the combustion chamber. The lower ends of the inclined conduits terminate in inlets located substantially evenly throughout the length of the combustion chamber whereby even distribution of the separated particles/fuel mixture is obtained.
Accordingly, it is a primary object of the present invention to provide novel and improved methods and apparatus for recycling particles separated from flue gas generated by a fluidized bed reactor in a manner in which the recycled separated particles and the fuel mixed therewith are substantially evenly distributed in the combustion chamber.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.